Due to the narrow emission peak of the quantum dot LED, the emission wavelength can depend on the size conditions so that the quantum dot LED is widely used in backlight products. However, due to the exposure of quantum dots to a water-oxygen environment, the fluorescence efficiency is irreversibly and rapidly decreased. The encapsulation of the quantum dots requires a good isolation of water and oxygen. The current quantum dot film is composed of PET with a barrier film. To make the quantum dot film have stable optical properties and service life, the oxygen barrier capability of the barrier film needs to be less than 10-1 cc/m{circumflex over ( )}2·day, and the water permeability needs to be less than 10-1 g/m{circumflex over ( )}2·day. In addition, because the quantum dots are sensitive to temperature and when the temperature is increased, the wavelength of the quantum dots will produce a red shift, and the luminous efficiency will also decrease.
As shown in FIG. 1, the conventional LED adopts a metal bracket 11 and a plastic bracket 12. The LED chip 13 is fixed on the metal bracket 11 and is connected with the metal bracket 11 through a gold wire 14. The phosphor and the silica gel 15 are encapsulated on the metal bracket 11 and the plastic bracket 12 with a packaging glue 16. Since the oxygen permeability and the water permeability of the plastic bracket 12 and the packaging glue 16 do not meet the requirements of the working environment of the quantum dot, the thermal conductivity coefficient of the plastic bracket 12 and the packaging glue 16 are lower, resulting in the increase of the quantum dot temperature and the luminous efficiency of the quantum dots is decreased with increasing temperature.
With reference to FIG. 2, the higher the temperature, the worse the water vapor transmission rate (WVTR) of the material, and the operating temperature of the LED is higher, thus raising a higher demand for the barrier property of the material. In order to achieve better barrier properties, it is necessary to adopt a thin film encapsulation to prepare a dense inorganic barrier layer to isolate water and oxygen. Due to the unevenness of the surface of the LED bracket, the use of sputter coating or PECVD may cause uneven thickness and cracking of the film due to unevenness of the surface of the bracket. Therefore, an atomic layer deposition (ALD) is currently used to realize the inorganic barrier layer. When using the ALD to deposit Al2O3, ZrO2, TiO2, generally H2O or O3 are injected. H2O or O3 will destroy the quantum dot at the high temperature (the process temperature is about 80° C.). In addition, the refractive index of Al2O3, ZrO2, TiO2 is higher (comparing to silica gel for packaging), the light extraction efficiency will be reduced.